Depends on the type of differental. A 14 bolt detroit locker doesn't require a carrier change
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Assuming your taking the full case detroit locker (the lunch box locker detroit makes is junk), it requires the ring gear to be removed from the old carrier, the pinion gear to be removed from the differental housing, and the gears to be set up preferably with new bearings. If you choose to do this yourself, make sure you check the contact pattern and backlash of the gears PRIOR to removal. This will let you know the gears have worn in together, or broken in, and let you set them up the same way. In turn, this will keep used gears from being noisy when reinstalled. This is also why I'd never buy used gears unless the provious owner can provide these specs for you.
Seriously though, unless you plan to go larger then 35's just put a Aussie lunch box locker in it. Neither a full case detroit or luck box style locker is selectable. The Deroit is stronger, but I don't think its an issue if your at 35's to run one. Heck, Nate is currently running one in his HP30 front and 8.8 rear on 36's. I know Aussie does not have a specific tire size max like other lunch box locker brands, but I wouldn't go over 35's on one for long term reliability. Another brand is the Spartan Locker. I had good luck with the one that I put in my Dana 44 Rear although it was a little noisy (by design, not a problem with it). The best thing about these lockers is they can be installed VERY easily in about an hour depending on your experience inside differentals.